The goal of this study was to obtain a complete description of the elastic modulus and hysteresis of the mantle tissue of the squid Loligo pealei over the entire functional region of the mantle. In addition, in vivo strains were measured to allow. calculations of the amount of energy stored and returned in each region of the mantle studied, and microscopic analysis of the tissue was carried out with the aim of correlating macroscopic properties with microscopic structure, The results of dynamic tissue tests indicate that mean elastic moduli for each of the 35 mantle positions tested ranged from 5.0x10(5) to 1.2x10(6) N m(-2). The elastic modulus varied within a narrow range, in no predictable manner, Mean hysteresis values for each position varied from 19.7 % to 27.3 % with no discernible patterns found either around or along the mantle. In vivo mantle strains peaked in the middle (lengthwise) of the mantle and declined towards both ends, and the absolute strains increased with increasing swimming velocity. Energy storage calculations showed that most energy was stored in the middle of the mantle, with an increase in storage with increased swimming velocity. Microscopic tissue analysis found direct correlations between macroscopic properties and microscopic characteristics, and electron microscopical analysis of all three types of intramuscular fibre revealed that all three types are collagenous in nature.